referring to the \(O(G_N^3)\)  post–Minkowskian Hamiltonian [1]}. Note that for \(k \le 3\)  no tail terms
contribute and the scattering angle stems from the potential contributions
only. The post–Minkowskian result of \(O(G_N^3)\)  [1]} has been checked to 6 PN in
[3]}.
